Metronome up to date

[Cressy Snr]

Hi.
There have been anumber of developments with the Metronome speaker


Martin King has come up with a proper baffle step correction circuit for the Metronome FE108EZ version. He visited Jim Shearer in New York, who had just completed a pair of the FE108EZ speakers http://www.diyaudio.com/forums/showthre ... ost1266342
a- to have a listen to them for himself and
b- to give Jim a hand with the positioning and set up of the Metronomes for his listening environment. They can be fussy little buggers in the initial set-up phase as Jim found out, but once set up they can be just left where they are forever with no problems.

The BSC circuit consists of a 1mH air cored inductor in parallel with about 2R5 of resistance in the positive leg of the speaker circuit.

According to Martin it produces a fantastic sound with the speakers about 12 inches out from the wall. Whilst they were at it Martin and Jim did a set of 1/3 octave in room measurements. The speakers are very evenly balanced with no peakiness and produce significant output at 40Hz before the steep roll off comes in.

Jim supports his below 40Hz with a Polk subwoofer for organ music and other big classical stuff that may have information in these very low regions but for general use, with the baseplate now a standard requirement for carpeted floors, a sub is not really that essential. According to Martin this is quite an accomplishment for such a small driver in such a relatively small enclosure. He has declared the Metronome concept a winner, which makes me dead chuffed really.

Of course in the speaker game you never get something for nothing so it follows that if they are capable of 40Hz in room then efficiency has to be down, "ye cannae change the laws of physics Captain Kirk" as Scotty would say. As a rough guess, they will probably be at about 89-90dB, which means that flea-powered 45 and 2A3 amps are still going to struggle despite the driver impedance never dropping below 6R. OTOH transmitter tube SE amps or push-pull and OTLs should be fine.

One or two people on this board and WD are considering building the Metronome FE108EZ for sons/daughters rooms so I present Martin's BSC spec as an aid to these people or anyone else considering bulding the smallest version.

PS Paul; now you have no excuse not to give your little Fostexes a good home

Regards

Steve.

[Scottmoose]

deleted

[Paul Barker]

I am actually using the 108's in mltl's designed by Jono for the ariel woofer. The ariel woofer sounded hopeless in them but the fostex sound gret inthem. obviously I am playing with stuff i don't comprehend but it soun ds ok so now I will throw in that baffle step in the hope it will lift the bass which is in short not sufficient.

The sound at present is adequate not boxy or confined.

Were I to win £36 million it would be Tightans, in the meantime these will do.

[Greg]

Paul,

Don't forget my tip (as Steve also found) of having a hard reflective surface under the port. This seriously lets bass be heard if it's there already but being muffled by carpet etc.

Best wishes,

Greg

[Cressy Snr]

Hi
Just an update on the now venerable old metronome FE108ES speakers.

Simon's comment on a certain thinness about my speakers in comparison to his big Fostex horns made me think seriously about putting the subwoofer back into the equation.

I hadn't used it it since putting the bit of wood beneath the bases of the two main enclosures but when someone points out something it is like having a cavity in a tooth; you can't help probing no matter how much you try not to.

I decided to try the sub out again, connected this time, to its high-level inputs, with a 4 pole Neutrik Speakon connector and a length of 4 core mains cable I had lying around.

The sub seems to do a far better job than it did before, giving a nice solid foundation to the music and reinforcing the atmospheric qualities of recordings where a strong ambience has been captured.

I took note of Martin King's findings when he visited the home of Jim Shearer in the USA and was able to measure 40Hz output from the cabs at around -6dB when placed on a hard surface. This was very helpful as it meant that I could roll the sub in at around 50Hz, playing at a very low level, instead of the 200Hz I had had it at before. Tuned in this way, the sub simply puts a solid foundation under the music and expands the soundstage a bit. Using a few descending bass runs, it was a doddle to set up. Unlike before when all I seemed to be doing was fiddle with it, I have this time been able to set and forget. The slight thinness has disappeared and the sound is fuller.

What I think was happening before was that the Mets were experiencing some kind of comb filter effect at the midbass/lowbass end due to the carpet absorbing some frequencies more than others. The result of this was that the sub was never going to be able to integrate properly with the mains. The wooden plates evened out the bottom end which gave the sub a fighting chance of augmenting the low frequencies without being audible.
The very low crossover frequency helps out too as the sub is now impossible to locate. The bass comes from wherever it has been placed in the soundstage and not from somewhere out to the right

I wouldn't bring the sub to any meets but in my room it is fine now.

Steve

[Cressy Snr]

Here's a sneek peek of some possible commercial FE108EZ Metronomes, caught on camera in a secret manufacturing facility in Siberia.

CNC machined cabs faced with ash....nice.

[simon]

Nice one Steve! You must be pretty proud?

Will you still come to our meets when you've made your fortune?

[Cressy Snr]

Hi Simon,

The metronome design is open-source, as are the larger variants designed by Scott and Dave (Planet10) Dlugos, so we are unlikely to get rich on the back of them. Nontheless, it is nice to have some interest from those people who can make them in larger numbers.

Steve

[simon]

No retirement yet then.

[Cressy Snr]

Hi Guys

Lots seem to be happening on the speaker front this festive season so I'll add in my two'pennorth.

Quite a simple addition to the speaker again just like the chopping board bases. The last of the slight shout that the FE108ES drivers exhibited in this cabinet has been banished by the simple addition of a 2R 10W wirewound resistor in the positive leg of each speaker.

This has had the effect of pushing the midrange back ever so slightly but by doing so, has allowed a more extended HF to show through.
The top had probably been there all the time but was being masked somewhat by the slight forwardness in the upper midrange.

The speaker now sounds nicely balanced and with the extended low end brought out by the hard bases the sub can be dialled in at 40Hz where it can't do any damage. All it does is simply add a solid foundation and an atmosphere on appropriate recordings.

The sub does not do much, which means that there is no longer the discontinuity at LF or the slowing of bass notes that there was this time last year.

A bigger pair next year will be the icing on the cake. I just hope that I won't be throwing away that lovely midrange tone the FE108ES has, by using FE167s or 207s.

Steve

[Nick]

drivers exhibited in this cabinet has been banished by the simple addition of a 2R 10W wirewound resistor in the positive leg of each speaker.

Want to remind us again why you have a push pull amp with a low output resistance .

[Cressy Snr]

drivers exhibited in this cabinet has been banished by the simple addition of a 2R 10W wirewound resistor in the positive leg of each speaker.

Want to remind us again why you have a push pull amp with a low output resistance .

Well I think the resistance is something to do with raising the Q of the driver or something. It is part of the baffle step correction circuit that Scott and Dave proposed for drivers using the Metronome enclosure.
There should also be a 1mH inductor in parallel with the resistance but I don't have those in at the moment.

It hasn't done anything to the bass, which is still tight as a gnats chuff and slams, as you would expect from a push pull amp. But the drivers were still a bit shouty with SE amps, so amp topology was not really the issue, more the tall, narrow shape of the cabinets. I know Paul's lash-ups at Egg 4 didn't shout like my drivers were prone to do when the going got rough, probably because of the wide baffles.

Perhaps a suprabaffle like the Cain & Cain Abby might be included with the bigger speakers to try and do away with need for the correction network. We'll see.

[colin.hepburn]

Hi All

Here's a sneek peek of some possible commercial FE108EZ Metronomes, caught on camera in a secret manufacturing facility in Siberia


i see the Metronomes in small production ? is there more info on this and perhaps the frugal horn as a flat pack i know that Dave / Scott are working on this so Anymore news on this coming up soon guys
thanks

[Paul Barker]

If u dont put the choke in u havent got baffle step correction you've just increased the impedance of the load on the amp and shared the signal across all frequencies with a resistor, resulting in less output.

Th epurpose of baffle step correction is the opposite of what you say you hear, the top is meant to recede slightly so the lower mids get back to the same level instead of falling off because of baffle size limitations. The choke is the main mechanism of limiting top end its effect is mitigated by the resistor which allows some high end information through unaffected by the choke.

Horns don't require this mod, Best way to correct the toppiness of such a driver is a front horn.

I think the metronomes started life as a voigt horn, that probably didnt't require baffle step correction, now that they are TL's everything is different.

My fostexes have always been protected from LF as the mids get nasty if you ask them to respond to LF of any significant amount.

They would make nice midrange drivers supported by a woofer as the OB's James designed for them.

The woofers from that project are up for grabs if you want some fun.

For the money it was a good system.

My gripe with the driver is what I like about it but it's it's downfall. It has such a lovely distinct tone, but isn't really a full range driver, thus needs suporting. Problem is no other speaker is tuned to that sound.

What is so much better about the Supravox AER combination is that the sonics of the two drivers dovetail. The little Fozzy just takes over your attention. Like those Yorkshire Terriers likes to be in charge.

If we use two or 3 drivers they must all sound same or you hear where they are, you only want to hear one voice.

[Cressy Snr]

If u dont put the choke in u havent got baffle step correction you've just increased the impedance of the load on the amp and shared the signal across all frequencies with a resistor, resulting in less output.

Th epurpose of baffle step correction is the opposite of what you say you hear, the top is meant to recede slightly so the lower mids get back to the same level instead of falling off because of baffle size limitations. The choke is the main mechanism of limiting top end its effect is mitigated by the resistor which allows some high end information through unaffected by the choke.

Horns don't require this mod, Best way to correct the toppiness of such a driver is a front horn.

Hi Paul

I'm well aware that I haven't got a BSC circuit but adding series resistance to these drivers reduces the motor damping slightly which, in these cabinets. appears to have pulled back the mids and removed the last bits of shout from the driver.

I would have thought that how a driver responds is all down to the cabinet it is mounted in. Don't forget that the Metronome cabinet is a highly resonant quarter wave system and relies entirely on controlled resonances to work properly so series resistances added to drivers in these types of cabs will have an effect, within the resonant system, which will not be the same at all frequencies. Efficiency will drop, yes but it is not quite that simple. They never are with speakers.

For instance an FE208Esigma driver in a 5 foot metronome cabinet requires around 4R in series with it to loosen it up and produce an even response.

I'm back to supporting the little driver with active bass..........Nice

Steve